Ejecting assembly for a surgical stapler

ABSTRACT

An end effector includes first and second jaws, a drive screw, a lead screw nut, and a drive beam. The drive screw is disposed within the first jaw. The lead screw nut defines a threaded bore that receives the drive screw. The lead screw nut is advanced along the drive screw as the drive screw is rotated in a first direction and is retracted along the drive screw as the drive screw rotates in a second direction. The drive beam is releasably coupled to the lead screw nut when the lead screw nut is in a retracted position. As the lead screw nut is advanced the drive beam is pulled by the lead screw nut. The drive beam is decoupled from the lead screw nut as the lead screw nut is advanced such that the lead screw nut is advanced relative to the drive beam.

BACKGROUND

Technical Field

The present disclosure relates to surgical apparatus, devices, and/or systems for performing endoscopic surgical procedures and methods of use thereof. More specifically, the present disclosure relates to electromechanical, hand-held surgical apparatus, devices, and/or systems configured for use with removable disposable loading units and/or single use loading units for clamping, cutting, and/or stapling tissue.

Description of Related Art

A number of surgical device manufacturers have developed product lines with proprietary drive systems for operating and/or manipulating electromechanical surgical devices. Some electromechanical surgical devices include a handle assembly, which is reusable, and replaceable loading units and/or single use loading units or the like that are selectively connected to the handle assembly prior to use and then disconnected from the handle assembly following use, in order to be disposed of or in some instances sterilized for re-use.

Many of these electromechanical surgical devices are relatively expensive to manufacture, purchase, and/or operate. There is a desire by manufacturers and end users to develop electromechanical surgical devices that are relatively inexpensive to manufacture, purchase, and/or operate.

Accordingly, a need exists for electromechanical surgical apparatus, devices and/or systems that are relatively economical to develop and manufacture, to store and ship, as well as economical and convenient to purchase and use from the end user's perspective.

SUMMARY

In an aspect of the present disclosure, an end effector includes first and second jaws moveable relative to one another, a drive screw, a lead screw nut, and a drive beam. The drive screw is disposed within the first jaw and defines a longitudinal axis. The lead screw nut defines a threaded bore that receives the drive screw therethrough. The lead screw nut is advanced along the drive screw as the drive screw is rotated in a first direction and is retracted along the drive screw as the drive screw rotates in a second direction that is opposite to the first direction. The drive beam is releasably coupled to the lead screw nut when the lead screw nut is in a retracted position. The drive beam is pulled by the lead screw nut as the lead screw nut is advanced towards a first advanced position. The drive beam decouples from the lead screw nut as the lead screw nut is advanced to the first advanced position such that the lead screw nut is advanced relative to the drive beam from the first advanced position to a second advanced position. The drive beam may define a passage that receives the drive screw therethrough.

In aspects, the end effector may include a sled that defines a channel that receives the drive screw and is configured to guide the sled along the drive screw. The lead screw may be spaced apart from and positioned proximal to the sled in the retracted position. The lead screw nut may engage a proximal surface of the sled at the first advanced position. The lead screw nut may push the sled distally as the lead screw nut is advanced from the first advanced position towards the second advanced position.

In some aspects, the first jaw may include a cartridge assembly that includes staples disposed therein. As the lead screw is advanced from the first advanced position towards the second advanced position, the sled may eject the staples from within the cartridge assembly towards the second jaw. The cartridge assembly may include a staple pusher associated with each of the staples such that the sled sequentially engages the staple pushers to eject the staples from within the cartridge assembly. When the lead screw nut is retracted to the first advanced position after pushing the sled, the sled may remain stationary in a position between the first and second advanced positions. When the lead screw nut is retracted from the first advanced position towards the retracted position, the lead screw nut pushes the drive beam towards the retracted position and couples to the drive beam.

In certain aspects, the end effector includes a latch having an elongated portion with proximal and distal ends. The proximal end of the elongated portion is pivotally coupled to the drive beam and the distal end of the elongated position includes a bridge. The bridge may be received within a notch defined by the lead screw nut when the lead screw nut is in the retracted position to couple the drive beam to the lead screw nut. When the lead screw nut is advanced towards the first advanced position, the bridge may be raised out of the notch to decouple the drive beam from the lead screw nut. When the lead screw nut is retracted from the first advanced position towards the refracted position, the bridge may be lowered into the notch to couple the drive beam to the lead screw nut.

In particular aspects, the end effector includes a cam member that is positioned adjacent the drive screw and defines a cam slot. The cam slot may have first portion that is parallel to the longitudinal axis of the drive screw and a second portion that extends distally from the first portion at an angle relative to and away from the longitudinal axis of the drive screw. The distal end of the elongated portion may include a pin that is slidably received in the cam slot. The bridge may be received in the notch when the pin is in the first portion of the cam slot and the bridge may be raised out of the notch as the pin slides distally along the second portion of the cam slot.

In another aspect of the present disclosure, a surgical instrument includes a handle, a shaft extending from the handle, and an end effector supported at a distal end of the shaft. The end effector may be any of the end effectors disclosed herein.

In yet another aspect of the present disclosure, a method of ejecting staples from a cartridge assembly includes providing an end effector, coupling a cartridge assembly to the first jaw, advancing a lead screw nut towards a first advanced position, and advancing the lead screw nut from the first advanced position. The end effector may be any of the end effectors disclosed herein. Advancing the lead screw nut towards a first advanced position is accomplished by rotating a drive screw in a first direction. The drive beam being pulled by the lead screw nut as the lead screw nut is advanced towards the first advanced position. The drive beam decoupling from the lead screw nut as the lead screw nut reaches the first advanced position. As the lead screw nut is advanced from the first position, the drive beam remains stationary and the lead screw nut pushes the sled through the cartridge assembly to sequentially eject the staples.

In aspects, the method includes retracting the lead screw nut from the second advanced position towards the first advanced position by rotating the drive screw in a second direction opposite the first direction. The sled remaining stationary as the lead screw nut is retracted. The method may include retracting the lead screw nut from the first advanced position towards a refracted position. The drive beam coupling to the lead screw nut as the lead screw nut is retracted from the first advanced position.

In some aspects, the drive beam decouples from the lead screw nut by raising a bridge of a latch that is operatively associated with the drive beam out of a notch defined by the lead screw nut.

In certain aspects, the drive beam couples to the lead screw nut by lowering a bridge of a latch operatively associated with the drive beam into a notch defined by the lead screw nut.

Further, to the extent consistent, any of the aspects described herein may be used in conjunction with any or all of the other aspects described herein.

BRIEF DESCRIPTION OF THE DRAWING

Various aspects of the present disclosure are described hereinbelow with reference to the drawings, which are incorporated in and constitute a part of this specification, wherein:

FIG. 1 is a perspective view of a surgical instrument in accordance with the presented disclosure with the parts separated;

FIG. 2 is a perspective view of the end effector of FIG. 1;

FIG. 3 is a side perspective view of the end effector of FIG. 2, with the upper jaw and the housing of the lower jaw removed, in a retracted position;

FIG. 4 is a top view of the end effector of FIG. 3;

FIG. 5 is a cross-sectional view taken along the line 5-5 of FIG. 4;

FIG. 6 is a side perspective view of the end effector of FIG. 2, with the upper jaw and the housing of the lower jaw removed, in a first advanced position;

FIG. 7 is a top view of the end effector of FIG. 6;

FIG. 8 is a cross-sectional view taken along the line 8-8 of FIG. 7;

FIG. 9 is a side perspective view of the end effector of FIG. 2, with the upper jaw and the housing of the lower jaw removed, in a second advanced position;

FIG. 10 is a top view of the end effector of FIG. 9; and

FIG. 11 is a cross-sectional view taken along the line 11-11 of FIG. 10.

DETAILED DESCRIPTION

Embodiments of the present disclosure are now described in detail with reference to the drawings in which like reference numerals designate identical or corresponding elements in each of the several views. As used herein, the term “clinician” refers to a doctor, a nurse, or any other care provider and may include support personnel. Throughout this description, the term “proximal” refers to the portion of the device or component thereof that is closest to the clinician and the term “distal” refers to the portion of the device or component thereof that is farthest from the clinician. The terms “left” and “right” refer to that portion of the electromechanical surgical system, apparatus and/or device, or component thereof, that are on the left and right (sides, respectively, from the perspective of the user facing the distal end of the electromechanical surgical system, apparatus and/or device from the proximal end while the surgical system, apparatus and/or device is oriented in non-rotational configuration.

Referring initially to FIG. 1, an end effector in accordance with an embodiment of the present disclosure is shown and generally designated 10. The end effector 10 may be connected to various surgical stapling instruments, e.g., manual or powered surgical stapling instruments. For illustrative purposes, the end effector 10 is described herein as configured to connect to a surgical apparatus or device in the form of an electromechanical, hand-held, powered surgical instrument 100. The surgical instrument 100 includes an adapter assembly (e.g., elongated body) 200 that connects to the end effector 10. The end effector 10 and the adapter assembly 200 are configured for actuation and manipulation by the electromechanical, hand-held, powered surgical instrument 100. In particular, the surgical instrument 100, the adapter assembly 200, and the end effector 10 are separable from each other such that the surgical instrument 100 is configured for selective connection with the adapter assembly 200, and, in turn, the adapter assembly 200 is configured for selective connection with any one of a plurality of different end effectors.

Briefly, the hand-held surgical instrument 100 includes a handle housing 102 having a lower housing portion 104, an intermediate housing portion 106 extending from or supported on lower housing portion 104, and an upper housing portion 108 extending from or supported on intermediate housing portion 106. Intermediate housing portion 106 and upper housing portion 108 are separated into a distal half-section 110 a that is integrally formed with and extending from the lower portion 104, and a proximal half-section 110 b connectable to the distal half-section 110 a by a plurality of fasteners. When joined, the distal and proximal half-sections 110 a, 110 b define a handle housing 102 having a cavity (not shown) therein in which a circuit board (not shown) and a drive mechanism (not shown) are situated.

It is contemplated that the handle can be manually operated, powered by a motor, and/or include a computerized controller or controllers. The end effector may be removable and replaceable and may house a staple cartridge that also may be removable and replaceable. The end effector and/or cartridge can include computerized microchips or mechanical features that are used in the identification of those components. Memory units can be included, such as EEPROMs, similar memory devices, and/or Dallas one wire chips. The adapter can be separately removable and replaceable, or be integral with the handle, and can have its own identification and/or memory features.

With continued reference to FIG. 1, the adapter assembly 200 is configured to communicate rotational forces provided by the surgical instrument 100 to the end effector 10. The adapter assembly 200 includes an elongate, substantially rigid, elongate body portion 210 having a proximal end 210 a and a distal end 210 b. A transmission housing 212 is connected to the proximal end 210 a of the elongate body portion 210 and is configured for selective connection to the surgical instrument 100. The adapter assembly 200 includes an articulating assembly 230 disposed at the distal end 210 b for coupling to the end effector 10. The transmission housing 212 of the adapter assembly 200 connects to a connecting portion 108 a of an upper housing portion 108 of the surgical instrument 100 via a shaft coupling assembly 214, which is supported at the proximal end 210 a.

Exemplary examples of electromechanical, hand-held, powered surgical instruments and adapters are disclosed in commonly owned and co-pending U.S. patent application Ser. No. 13/331,047, filed Dec. 20, 2011 and published as U.S. Patent Pub. No. 2012/0089131 on Apr. 12, 2012, and Ser. No. 13/484,975, filed May 31, 2012 and published as U.S. Patent Pub. No. 2012/0253329 on Oct. 4, 2012, the contents of each are hereby incorporated by reference in their entirety.

Referring to FIGS. 1 and 2, the end effector 10 includes a first jaw 12 that includes a carrier or housing 18 which is configured to releasably couple to a cartridge assembly 16 (FIG. 2). The end effector 10 includes a second jaw 14 in the form of an anvil. The cartridge assembly 16 houses one or more fasteners 310 (FIG. 3) that are disposed therewithin and is configured to deploy the fasteners 310 upon firing of instrument 100. The second jaw 14 is mounted to the end effector 10 and is movable with respect to the first jaw 12 between an open position, wherein the second jaw 14 is spaced-apart from cartridge assembly 16, and a closed position, wherein the second jaw 14 is in close cooperative alignment with cartridge assembly 16, to clamp tissue therebetween. The second jaw 14 may be pivotally mounted to the first jaw 12.

Referring to FIGS. 3-5, the jaw housing 18 includes a drive assembly including an axial drive screw 20 for transmitting the rotational drive forces exerted by one or more drive shafts (not explicitly shown) of the adapter 200 (FIG. 1) to a drive screw nut 38 during a stapling procedure. The drive screw 20 is rotatably supported in the jaw housing 18 and includes a threaded portion 26 and a proximal engagement portion 27. The threaded portion 26 of the drive screw 20 extends through a bore 29 (FIG. 5) defined through a drive beam 28, such that the drive screw 20 rotates freely within the bore 29 of the drive beam 28. The drive beam 28 travels in a longitudinal direction along a longitudinal axis “A-A” defined by the drive screw 20, as will be described in detail below.

The drive beam 28 is slidably and non-rotatably disposed within the jaw housing 18 and includes a vertical support strut 34 and an abutment surface 36 that engages a drive screw nut 38. The drive beam 28 also includes a cam member 40 disposed on top of the vertical support strut 34. The vertical strut 34 is translatable through a longitudinal slot 44 (FIG. 2) defined by an exterior camming surface 42 (FIG. 2) of the second jaw 14. In use, the cam member 40 engages the exterior camming surface 42 of the second jaw 14 and translate therealong to progressively close the second jaw 14 relative to the first jaw 12 to capture body tissue therebetween before ejecting the fasteners 310 (FIG. 5).

Continuing with reference with FIGS. 3-5, a latch 46 is shown including first and second elongated portions, links, or bars 48 a, 48 b, which are pivotally coupled at their proximal ends to the drive beam 28 via a first pin 50. The pin 50 extends through the vertical support strut 34 adjacent a proximal end of the drive beam 28.

The first and second elongated portions 48 a, 48 b are connected to one another at their distal ends 52 a, 52 b via bridge 54 and a second pin 58. The second pin 58 includes side protrusions 57 a, 57 b that extend laterally from the distal ends 52 a, 52 b of the first and second elongated portions 48 a, 48 b, and the bridge 54. The bridge 54 is movable in and out of engagement with a recess 56 that is formed in an outer surface of the drive screw nut 38 and that is defined adjacent a proximal end thereof.

First and second cam members 60 a, 60 b are positioned within the jaw housing 18 and are coupled, e.g., screws, rivets or the like, to an internal wall of the jaw housing 18. Each of the first and second cam members 60 a, 60 b define a respective first and second cam slots 61 a, 61 b therein. The first and second cam slots 61 a, 61 b each include a respective first cam portion 62 a, 62 b and a respective second cam portion 64 a, 64 b. In embodiments, only one of the cam members 60 a, 60 b is utilized and the other is omitted. Moreover, while the first and second cam slots 61 a, 61 b are described herein as being defined on the first and second cam members 60 a, 60 b, it is in the purview of the instant disclosure that the first and second cam members 60 a, 60 b can be omitted and the first and second cam slots 61 a, 61 b can simply be defined within the internal wall of the jaw housing 18.

The drive screw nut 38 includes a threaded bore 39 (FIG. 5) that is threadably coupled to the threaded portion 26 of the drive screw 20 such that as the drive screw 20 is rotated, the drive screw nut 38 translates along the longitudinal axis “A-A” defined by the drive screw 20. The drive screw nut 38 longitudinally translates the drive beam 28 when the drive screw nut 38 is coupled to the drive beam 28 via the bridge 54, as will be described in greater detail below. The drive screw nut 38 is configured to engage the sled 22 of the cartridge assembly 16 (FIG. 2) to eject the fasteners 310 from the cartridge 16 as detailed below.

The sled 22 includes outwardly and laterally extending flanges 24 and defines a channel 25 (FIG. 9) therebetween. The sled 22 is positioned over the drive screw 20 receiving the drive screw 20 in the channel 25 such that the channel 25 guides translation of the sled 22 along the longitudinal axis A-A. The sled 22 has upstanding cam wedges 23 configured to exert a fastener driving force on pushers 312 of the cartridge assembly 16, which drive the fasteners 310 from cartridge assembly 16. Advancement of the drive screw nut 38 through cartridge assembly 16 translates the actuation sled 22 such that the angled leading edges of cam wedges 23 sequentially contact the pushers 312 causing the pushers 312 to translate vertically, thereby urging the fasteners 310 from cartridge assembly 16.

In use, initially, the drive beam 28 of the drive assembly is in a home or retracted position with the bridge 54 of the latch 46 positioned within the recess 56 of the drive screw nut 38 as shown in FIGS. 3-6. In this position, a user can couple a fresh, new, unspent cartridge assembly 16 to the jaw housing 18 of the first jaw 12.

When the surgical stapler is fired, the drive screw 20 is rotated, e.g., in a clock-wise direction, and the drive screw nut 38 advances distally. As the drive screw nut 38 advances, the drive screw nut 38 pulls the drive beam 28 distally to close the second jaw 14 by translating the vertical support strut 34 through the slot 44 such that the cam member 40 cams against external camming surface 42 to approximate the first and second jaws 12, 14. Moreover, as the drive beam 28 is advanced, the side protrusions 57 a, 57 b of the second pin 58 slide through the first and second cam slots 61 a, 61 b of the first and second cam members 60 a, 60 b. The bridge 54 of the latch 46 remains positioned within the recess 56 of the drive screw nut 38 as the side protrusions 57 a, 57 b of the second pin 58 slide along the first cam portions 62 a, 62 b of the first and second cam slots 61 a, 61 b. When the side protrusions 57 a, 57 b of the second pin 58 begin to slide along the second cam portions 64 a, 64 b of the first and second cam slots 61 a, 61 b, the first and second elongated portions 48 a, 48 b of the latch 46 begin to pivot about the drive beam 28 via first pin 50 to gradually raise the bridge 54 from within the recess 56 of the drive screw nut 38.

Referring to FIGS. 6-8, the drive beam 28 continues to advance distally towards a first advanced position such that the bridge 54 is no longer positioned within the recess 56 (e.g., the side protrusions 57 a, 57 b of the second pin 58 have slid to a distal end of the second cam portions 64 a, 64 b). At this point, the lead screw nut 38 continues to advance distally, without the drive beam 28. As the lead screw nut 38 advances distally, the lead screw nut 38 engages the sled 22 to advance or push the sled 22 distally towards a second advanced position. As the sled 22 advances, the sled 22 engages the pushers 312 via the cam wedges 23 to eject the fasteners 310 from the cartridge assembly 16. It is within the scope of this disclosure that the lead screw nut 38 may pull the drive beam 28 and simultaneously push the sled 22.

Once the cartridge assembly 16 is spent, or the stapling procedure is stopped, the drive screw 20 is rotated in an opposite direction, e.g., in a counter clock-wise direction, which retracts the drive screw nut 38 towards the retracted position. As the drive screw nut 38 retracts, the drive screw nut 38 contacts the abutment surface 36 of the drive beam 28 to push or retract the drive beam 28. As the drive beam 28 is retracted by the drive screw nut 38, the side protrusions 57 a, 57 b of the second pin 58 slide proximally along the second cam portions 64 a, 64 b of the first and second cam slots 61 a, 61 b causing the first and second elongated portions 48 a, 48 b of the latch 46 to pivot about the drive beam 28 via first pin 50. The second cam portions 64 a, 64 b seat the bridge 54 back into the recess 56 of the drive screw nut 38. In addition, the weight of the bridge 54 and/or the second pin 50 may assist in seating the bridge 54 back into the recess 56 of the drive screw nut 38. It will be appreciated that when the drive screw nut 38 is retracted, the sled 22 remains in a distal position.

Once the drive screw nut 38 and drive beam 28 are in the retracted position, a fresh cartridge assembly 16 can be coupled to the jaw housing 18 of the jaw 12 and the surgical stapler can then be fired again.

From the foregoing and with reference to the various figure drawings, those skilled in the art will appreciate that certain modifications can also be made to the present disclosure without departing from the scope of the same. For example, the end effector 10 can be configured as an integral unit in any of the embodiments disclosed herein. The end effector 10 can be configured for use with a console and/or surgical robot, in any of the embodiments disclosed herein.

In embodiments, a resilient member (not shown) may be provided on the latch 46 that is configured to urge the bridge 54 downwardly into recess 56 of the drive screw nut 38.

While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Any combination of the above embodiments is also envisioned and is within the scope of the appended claims. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto. 

What is claimed is:
 1. An end effector comprising: first and second jaws moveable relative to one another; a drive screw disposed within the first jaw and defining a longitudinal axis; a lead screw nut defining a threaded bore, the threaded bore receiving the drive screw, the lead screw nut is advanced along the drive screw as the drive screw is rotated in a first direction and is retracted along the drive screw as the drive screw is rotated in a second direction opposite the first direction; and a drive beam releasably coupled to the lead screw nut when the lead screw nut is in a retracted position, the drive beam being pulled by the lead screw nut as the lead screw nut is advanced towards a first advanced position, the drive beam decoupling from the lead screw nut as the lead screw nut is advanced to the first advanced position such that the lead screw nut is advanced relative to the drive beam from the first advanced position to a second advanced position.
 2. The end effector of claim 1, wherein the drive beam defines a passage that receives the drive screw therethrough.
 3. The end effector of claim 1 further comprising a sled defining a channel, the channel receiving the drive screw and configured to guide the sled along the drive screw.
 4. The end effector of claim 3, wherein in the retracted position of the lead screw nut, the lead screw nut is spaced apart from and positioned proximal to the sled.
 5. The end effector of claim 3, wherein the lead screw nut engages a proximal surface of the sled at the first advanced position, the lead screw nut pushing the sled distally as the lead screw nut is advanced from the first advanced position towards the second advanced position.
 6. The end effector of claim 5, wherein the first jaw includes a cartridge assembly including staples disposed therein and as the lead screw nut is advanced from the first advanced position towards the second advanced position the sled ejects the staples from within the cartridge assembly towards the second jaw.
 7. The end effector of claim 6, wherein the cartridge assembly includes a staple pusher associated with each of the staples, the sled sequentially engaging the staple pushers to eject the staples from within the cartridge assembly.
 8. The end effector of claim 5, wherein, when the lead screw nut is retracted to the first advanced position after pushing the sled, the sled remains stationary in a position between the first and second advanced positions.
 9. The end effector of claim 8, wherein when the lead screw nut is retracted from the first advanced position towards the retracted position, the lead screw nut pushes the drive beam towards the retracted position and couples to the drive beam.
 10. The end effector of claim 1 further comprising a latch including an elongated portion, the elongated portion having proximal and distal ends, the proximal end of the elongated portion pivotally coupled to the drive beam, the distal end of the elongated portion including a bridge, the bridge received within a notch defined by the lead screw nut when the lead screw nut is in the retracted position to couple the drive beam to the lead screw nut.
 11. The end effector of claim 10, wherein when the lead screw nut is advanced towards the first advanced position the bridge is raised out of the notch to decouple the drive beam from the lead screw nut.
 12. The end effector of claim 10, wherein when the lead screw nut is retracted from the first advanced position towards the retracted position, the bridge is lowered into the notch to couple the drive beam to the lead screw nut.
 13. The end effector of claim 10 further comprising a cam member positioned adjacent the drive screw defining a cam slot, the cam slot having a first portion parallel to the longitudinal axis of the drive screw and a second portion extending distally from the first portion at an angle relative to and away from the longitudinal axis of the drive screw, wherein the distal end of the elongated portion includes a pin that is slidably received in the cam slot.
 14. The end effector of claim 13, wherein the bridge is received in the notch when the pin is in the first portion of the cam slot and wherein the bridge is raised out of the notch as the pin slides distally along the second portion of the cam slot.
 15. A surgical instrument comprising: a handle; a shaft extending distally from the handle; and an end effector supported at a distal end of the shaft, the end effector comprising: first and second jaws moveable relative to one another; a drive screw defining a longitudinal axis disposed within the first jaw; a lead screw nut defining a threaded bore, the threaded bore receiving the drive screw, the lead screw nut is advanced along the drive screw as the drive screw is rotated in a first direction and is retracted along the drive screw as the drive screw is rotated in a second direction opposite the first direction; and a drive beam releasably coupled to the lead screw nut when the lead screw nut is in a retracted position, the drive beam being pulled by the lead screw nut as the lead screw nut is advanced towards a first advanced position, the drive beam decoupling from the lead screw nut as the lead screw nut is advanced to the first advanced position such that the lead screw nut is advanced relative to the drive beam from the first advanced position to a second advanced position.
 16. A method of ejecting staples from a cartridge assembly, the method comprising: providing an end effector including: a first jaw; a drive screw disposed within the first jaw and defining a longitudinal axis; a lead screw nut defining a threaded bore, the threaded bore receiving the drive screw; and a drive beam releasably coupled to the lead screw nut in a retracted position; coupling a cartridge assembly to the first jaw, the cartridge assembly including staples; advancing the lead screw nut towards a first advanced position by rotating the drive screw in a first direction, the drive beam pulled by the lead screw nut, the drive beam decoupling from the lead screw nut as the lead screw nut reaches the first advanced position; and advancing the lead screw nut from the first advanced position towards a second advanced position, the drive beam remaining stationary, the lead screw nut pushing a sled through the cartridge assembly to sequentially eject the staples.
 17. The method of claim 16, further comprising retracting the lead screw nut from the second advanced position towards the first advanced position by rotating the drive screw in a second direction opposite the first direction, the sled remaining stationary as the lead screw nut is retracted.
 18. The method of claim 17, further comprising retracting the lead screw nut from the first advanced position towards a retracted position and the drive beam coupling to the lead screw nut as the lead screw nut is retracted from the first advanced position.
 19. The method of claim 16, wherein decoupling the drive beam includes raising a bridge of a latch operatively associated with the drive beam out of a notch defined by the lead screw nut.
 20. The method of claim 18, wherein coupling the drive beam to the lead screw nut includes lowering a bridge of a latch operatively associated with the drive beam into a notch defined by the lead screw nut.
 21. A surgical end effector comprising: first and second jaws moveable relative to one another; a driver element disposed within the first jaw and defining a longitudinal axis, the driver element having a constant diameter between proximal and distal ends thereof, the driver element being a threaded member; an internally threaded nut threadably engaged with the driver element; and a drive member releasably coupled to the driver element, the drive member being pulled by the driver element towards a first advanced position and decoupling from the driver element upon reaching a predetermined position corresponding to a closed position of the first and second jaws, the surgical end effector including a sled for firing staples from the first jaw, the driver element moving the sled to fire staples after the drive member is decoupled from the driver element, the drive member having the shape of an I-beam, the drive member releasably coupled to the nut.
 22. The surgical end effector according to claim 21, wherein the drive member is releasably coupled to the nut by a latch.
 23. The surgical end effector according to claim 22, further comprising a cam for disengaging the latch.
 24. The surgical end effector according to claim 21, wherein the nut is advanced along the driver element as the driver element is rotated in a first direction and is retracted along the driver element as the driver element is rotated in a second direction opposite the first direction. 